master key

noun
a key that will open a number of different locks, the proper keys of which are not interchangeable.

Origin:
1570–80

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Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
master key
 
n
Also called: pass key a key that opens all the locks of a set, the individual keys of which are not interchangeable

Collins English Dictionary - Complete & Unabridged 10th Edition
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Example sentences
In an individually-keyed padlock system, there is no master key, and all of the
  locks must be opened with their own key.
The contractor shall provide padlocks for each disconnect switch and receptacle
  box with a master key for all locks.
He photocopies it and emails the scan, distributing a master key that can
  access a whole floor.
Using his master key, the officer released the lock.
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